Abstract
Introduction
Pedicle screw instrumentation has been shown to provide better curve correction with solid three-column fixation in adolescent idiopathic scoliosis (AIS) surgery. The levels of spinal segments to be fused are based on Lenke classification. However, the optimal anchor density of fixation points in AIS surgery to achieve cost effective curve correction remains unclear. The purpose of the study is to analyze the correlation between curve correction and anchor density in pedicle screw based posterior fusion of AIS.
Material and Methods
From Jan. 2003 to Dec. 2008, 121 consecutive AIS patients underwent primary posterior fusion with pedicle screw based fixation and followed up for a minimum of 24 months were reviewed. Anchor density was defined as the number of screws per fused spinal segment. Radiographs were assessed at preoperative, postoperative 0, 3, 6, 12 and every 12 months until last follow up. The relation between anchor density and correction rate in Lenke subgroups were analyzed.
Results
There were 14 male and 107 female patients enrolled and aged 14.1 years old at the time of surgery. The number of Lenke type 1, 2, 3, 4, 5 and 6 curve patients were 67, 22, 9, 2, 14 and 7 respectively. For all patients, the mean correction rate was 63.1 ± 15.8% in all structural curves and 67.0 ± 12.0% in major curves only. The mean anchor density was 1.30 ± 0.18. There was no correlation between anchor density and major curve correction rate (r=0.24, p = 0.01). Patients of anchor density >1.30 (=mean anchor density of all patients) had similar correction rate with patients of anchor density <=1.30 in the major curves (67.9 ± 13.2% vs 66.0 ± 10.4%, p = 0.38). For Lenke type 1, 2 and 3 curves, there was no correlation between major curve correction rate and anchor density (Lenke 1: r=0.02, p = 0.88; Lenke 2: r=0.30, p = 0.18; Lenke 3: r = −0.20, p = 0.60) with mean anchor density of 1.29 ± 0.15, 1.23 ± 0.17 and 1.23 ± 0.10 respectively. For Lenke type 5 curves, the major curve correction rate was positively correlated with anchor density (r=0.61, p = 0.02) with mean anchor density of 1.51 ± 0.23.
Conclusion
There was no significant correlation between curves correction rate and anchor density in pedicle screw based instrumentation of adolescent idiopathic scoliosis surgery. Although for major thoracolumbar/lumbar curves, anchor density may play a role in curve correction, further investigation is still needed.